A typical power transmission system of a wheel loader generally includes: an engine mounted to a rear-vehicle-body frame; a transmission configured to receive rotation power of the engine to shift gears; a rear axle that is attached to the rear-vehicle-body frame transmission in the rear of the transmission and houses a differential; a propeller shaft that connects an output shaft of the transmission to an input shaft of the differential; a pair of axle shafts that respectively project from the rear axle to the right and left sides thereof; and rear tires supported by outer ends of the axle shafts (for instance, Patent Literature 1).
In a small-sized wheel loader, the transmission is often provided by a hydraulic static transmission (HST). In a middle-sized wheel loader, a so-called automatic transmission in which a torque converter and a planetary mechanism are combined is mainly used.